1. Field of the Invention
This invention relates to capacitive pressure transducers and more to such a transducer for use in respirator apparatus which provides an electrical control signal for controlling the supply of a gas such as oxygen to a patient in response to the inspiratory breathing cycles of such patient.
2. Description of the Related Art
Respiratory Apparatus has been developed in the prior art which responds to the breathing cycles of the patient and supplies oxygen in response to such breathing cycles. In such devices, the breathing cycles are generally sensed by a pressure transducer which provides an electrical output in accordance with such breathing. Such an apparatus is described in U.S. Pat. No. 4,612,928 issued Sep. 23, 1986 to Tiep et al. Other such devices are described in the various references cited in the Tiep patent. The pressure transducers employed in such prior art devices generally operate in response to both the inspiration and expiration of the patient. As oxygen is to be supplied only in accordance with the inspiration demand of the patient, the expiration input is extraneous and it has been found tends to decrease the accuracy of the control signal for effecting the oxygen supply. This is particularly significant in the case of capacitive transducers in view of the fact that the diaphragm forming one of the capacitive plates of the transducer is driven in response to the expiration of the breathing cycle away from its neutral position and may return late to such position such that it will be seen by the system as an inspiration.